MediumBiologyHigh School (9–10)GeneralLife Processes › Transport in Living OrganismsConceptualBoard Exam
In the evening, Leela cuts the stem of a potted tomato plant close to the soil…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In the evening, Leela cuts the stem of a potted tomato plant close to the soil. By the next morning, a drop of sap has collected on the cut stump, which has no leaves at all. (a) What pushed the water up? (b) Why could it not be the transpiration pull? (c) Which force lifts most of the water in a tall tree at noon?
Need a reminder? The key ideaShow
Xylem carries water and minerals up from the roots. Root pressure pushes water up, mostly at night. In the day, transpiration from the leaves pulls water up the xylem. Phloem carries food (sucrose) to where it is needed, up or down, using energy from ATP. This is translocation.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The push. The roots took in minerals from the soil, so water moved into the roots. This root pressure pushed the water up the xylem of the stump.
Step 2. Not transpiration. The transpiration pull comes from water evaporating at the leaves. The stump has no leaves, so there is no pull.
Step 3. A tall tree. At noon, transpiration from many leaves is fast, and the transpiration pull lifts most of the water.
Answer: (a) Root pressure. (b) There are no leaves to lose water, so there is no pull. (c) The transpiration pull.
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